1. Field of the Invention
The present invention relates to a printing apparatus and a discharge inspection method.
2. Description of the Related Art
In an ink-jet printing head, discharge failure sometimes occurs in all or some nozzles due to clogging of nozzles with foreign substances, bubbles entering ink supply channels, changes in the wettability of nozzle surfaces, or the like. It is an important challenge for such a printhead to specify a nozzle subjected to discharge failure and reflect the failure in image supplement or recovery operation for the printhead.
In consideration of this challenge, Japanese Patent Laid-Open No. 2007-290361 has proposed a method of inspecting a nozzle subjected to discharge failure from the manner of changes in temperature obtained by detecting the temperature information of each nozzle by providing a temperature detection element which is formed for each print element by using a thin-film resistive element through an insulating film in a print element substrate.
Japanese Patent Laid-Open Nos. 2007-331193 and 2008-000914 each have proposed an inspection method of detecting the presence of a change in temperature drop (to be referred to as a feature point hereinafter) in the temperature drop process represented by a temperature curve and determining normal discharge if a feature point appears. It is thought that this feature point appears when the trailing end of a discharged droplet comes into contact with a print element to lower the temperature of the print element.
According to Japanese Patent Laid-Open Nos. 2007-331193 and 2008-000914, to facilitate detection of a feature point as a slight change, second order differential computation is performed to enhance the change to detect a feature point, thereby determining, based on the result, whether the discharge operation is normal discharge. At this time, however, noise is also simultaneously enhanced. This will lead to a determination error unless a noise component is made sufficiently smaller than a waveform change as a feature point. Although it is possible to obtain a feature point based on a curvature change of acquired temperature information. In this case, like the above case, a determination error occurs unless noise is made sufficiently smaller than a curvature change.